Mechanical and Electrical Properties of Mesoscopic Wires
Sammanfattning: The mechanical and electrical properties of mesoscopic wires have been studied theoretically using a free electron model. When a mesoscopic wire is elongated the conductance decreases in steps. Each step is accompanied by an abrupt change in the force. We have shown that the electronic contribution to the force show abrupt changes, at each conductance step, of the same magnitude as the experimentally recorded, force fluctuations.An electromagnetic field may cause coupling between the electron modes in the wire. In a wire of varying width this induces backscattering of electrons. We have calculated the photoconductance, the change in conductance due to a microwave field, in such a wire. The photoconductance can be used to investigate the electronic spectrum. If the energy difference between two modes is constant an electromagnetic field in resonance with the modes causes Rabi oscillations in the population amplitudes of the two modes. We have shown that this increases the force and affects the rigidity in a mesoscopic wire. Since the electromagnetic field only affects the electronic subsystem of the wire, not the atomic, an experiment along these lines might give further insight into which contribution to the force is responsible for the force fluctuations: the one from the electronic subsystem or the one from the atomic rearrangements. A magnetic field perpendicular to the wire cross-section will influence the electronic spectrum of the wire. This will in turn affect both the conductance and the force in the wire, giving more steps, accompanied by abrupt changes. A magnetic field is an equilibrium method to control the number of modes. We have also investigated the transport properties of a one-dimensional channel with a wider, straight region irradiated by a microwave field. The interplay between interference effects and resonance phenomena manifests itself, resulting in a new behaviour of the conductance. We have shown that the transport properties of the system can be affected by changing the frequency and the amplitude of the external field and that, for certain combinations of these parameters, electron transport through the system is completely blocked.
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